Preface. This is clearly a pipedream. Surely the authors know this, since they say that the energy needed to run direct air capture machines in 2100 is up to 300 exajoules each year. That’s more than half of global energy consumption today. It’s equivalent to the current annual energy demand of China, the US, the EU and Japan combined. It is equal to the global supply of energy from coal and gas in 2018.
That’s a showstopper. This CO2 chomper isn’t going anywhere. It simply requires too much energy, raw materials, and an astounding, impossibly large-scale rapid deployment of 30% a year to be of any use.
Reaching 30 Gt CO2/yr of CO2 capture – a similar scale to current global emissions – would mean building some 30,000 large-scale DAC factories. For comparison, there are fewer than 10,000 coal-fired power stations in the world today.
The cement and steel used in DACCS facilities would require a great deal of energy and CO2 emissions that need to be subtracted from whatever is sequestered.
Nor can the CO2 be stored in carbon capture sorbents – these are between the research and demonstration levels, far from being commercial, and are subject to degradation which would lead to high operational and maintenance costs. Their manufacture also releases chemical pollutants that need to be managed, adding to the energy used even more. Plus sorbents can require a great deal of high heat and fossil fuel inputs, possibly pushing up the “quarter of global energy” beyond that.
As far as I can tell the idea of sorbents, which are far from being commercial and very expensive to produce, is only being proposed because there’s not enough geological storage to put CO2.
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